The number of U.S. adults who are diagnosed with colorectal cancer before age 50 is on the rise, a new study finds.

Researchers analyzed information from more than 1 million colorectal cancer cases that were diagnosed from 2004 to 2013, using the U.S. National Cancer Data Base.

During that time, the number of colorectal cancer cases in people under 50 years old increased by 11.4 percent, which translates to an increase of about 136 cases each year during the study period, according to the study, which was presented in San Diego on May 24 at Digestive Disease Week, a meeting of researchers and doctors focused on digestive diseases.

In contrast, the number of colorectal cancer cases in adults ages 50 and older decreased by 2.5 percent during the study period, the researchers said.

In addition, a higher percentage of patients under age 50 were diagnosed with advanced colorectal cancer (stages 3 or 4), compared with the percentage of older patients who were diagnosed at these later stages.

More effort is needed to fight colorectal cancer in younger adults, the researchers said. Current U.S. guidelines, from the Preventive Services Task Force, recommend that adults start getting screened for colorectal cancer at age 50.

"While the health care system has done a great deal to address colorectal cancer in people over 50 … our findings show that much more needs to be done to fight this cancer in people under 50, a group not normally considered at risk," said Dr. Elie Sutton, the study's lead author and a research fellow at Mount Sinai West Hospital in New York. "It's critical that we reverse this trend so that we are able to reduce, and hopefully eliminate, [colorectal cancer] in all populations, regardless of age." [10 Do's and Don'ts to Reduce Your Risk of Cancer]

The reason for the increase in cases in younger people is not unknown, Sutton said. The American Cancer Society notes that U.S. obesity rates have increased in recent years and that obesity is a major risk factor for colorectal cancer.

Colorectal cancer screening guidelines "may need to be revisited, in order to catch cases earlier," Sutton and her colleagues said.

But for now, the researchers stress that doctors should be more vigilant about detecting colorectal cancer symptoms in younger patients. "Don't hesitate to move forward with a colonoscopy" in younger patients who have symptoms of colorectal cancer, such as rectal bleeding, Sutton said.

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